Using Porteus Kiosk [PK] version 4.2.0, with Chrome, I am getting a 'Your connection is not private' warning for the site https://llv.net.au
Specific error is: NET::ETT_CERTIFICATE_TRANSPARENCY_REQUIRED
I do not get this certificate error on Windows with Chrome v55, or Ubuntu with Chrome v56.

If I accept the certificate, I can see that the certificate is supplied by thawte.

i can confirm that Chrome 55.x works fine on this website. If 'automatic updates' are not an option then please enable free trial on your kiosks and wait till next public version is released. Optionally you could switch to Firefox, customize the ISO yourself or buy a custom build with latest Chrome.